Rocket nozzle with automatically adjustable auxiliary nozzle portion



Dec. 1967 J. H. ALTSEIMER 3,

ROCKET NOZZLE WITH AUTOMATICALLY ADJUSTABLE AUXILIARY NOZZLE PORTION Original Filed Sept. 14, 1962 INVENTOR. JOHN H. ALTSEIMER United States Patent 3,358,933 ROCKET NOZZLE WITH AUTOMATICALLY AD- JUSTABLE AUXILIARY NQZZLE PORTION John H. Altseimer, Carmichael, Calif., assignor to Aerojet-General Corporation, Azusa, Calif a corporation of Ohio Original application ept. 14, 1962, Ser. No. 223,646, now Patent No. 3,249,306, dated May 3, 1966. Divided and this application Mar. 7, 1966, Ser. No. 557,846

2 Claims. (Cl. 239-26543) This is a division of application Ser. No. 223,646, filed Sept. 14, 1962, now US. Patent 3,249,306 issued May 3, 1966.

The present invention relates to rocket engines and particularly to the rovision of automatically expandable nozzles for such engines.

To obtain maximum efliciency from a rocket engine, the nozzle thereof requires to be designed to meet special conditions and such conditions cannot be met satisfactorily by using a nozzle of fixed size particularly in rockets designed for flight to high altitudes or into outer space.

The pressure of the atmosphere becomes less with height, for instance, and a vacuum exists beyond the earths atmosphere. A rocket exhaust nozzle has the maximum efiiciency at any altitude when the nozzle gas pressure at the nozzle exit is exactly equal to the atmospheric pressure. The exit nozzle gas pressure decreases as the ratio of nozzle exit to nozzle throat area increases. Therefore, as a rocket rises to higher altitudes, it is beneficial to have the nozzle area ratio increase so that the exit pressure continuously equals the atmospheric pressure.

High altitude and space rockets are built up of a number of stages and, since the lowest possible dead weight should be carried, an expandable rocket nozzle that can be fitted into a smaller than usual rocket casing is a desirable feature.

It is an object of the present invention to provide an automatically adjustable nozzle construction for a rocket engine, the size of the nozzle increasing to a maximum nozzle diameter as the ambient pressure decreases.

A further object of the invention is to provide an automatically adjustable nozzle construction for a rocket engine and provide means for taking axial loads on the nozzle, which means may also be arranged to carry fluids utilized to cool the nozzle.

Another object of the invention is to provide a rocket engine nozzle construction which may be reduced in length as well as in diameter before firing of the rocket.

Still further objects and features of the invention will hereinafter appear from the following description read together with the accompanying illustrative drawings, wherein:

FIG. 1 is a side view of an adjustable rocket engine nozzle incorporating the novel features of the invention, indicating the variation in the diameter of the exhaust end of the nozzle, the full lines showing the adjustable portion of the nozzle in retracted or firing position and the dotted lines indicating partial and fully expanded positions;

FIG. 2 is a fragmentary side elevation of the adjustable nozzle shown in FIG. 1 but drawn on a larger scale, the upper portion of the figure showing the outside of the nozzle while the lower portion of the figure shows the inside of the nozzle lined with cooling tubes;

FIG. 3 is a rear fragmentary end view of the nozzle construction of FIG. 2 but shown in expanded position;

FIG. 4 is a fragmentary forward end view of the nozzle 3,358,933 Patented Dec. 19, 1967 construction shown in FIG. 2 shown in retracted condition;

FIG. 5 is a fragmentary side view, partly in section, showing a nozzle fitted with a skirt of flexible material being in its initial tucked-in position at the right sectioned half of the figure, and fully extended in the left hand half of the figure.

Referring now to FIG. 1, the numeral 10 indicates the fixed portion of a rocket engine nozzle fitted with an ex terior peripheral flange 11 at its outlet end. An expandable nozzle portion or skirt generally indicated by numeral 12 is fitted at its forward end to a mounting flange 12' which may be bolted or otherwise secured to flange 11.

Nozzle portion or skirt 12 is formed as a cylindrical member from a material which is highly flexible and easily bent or folded. The material may be metallic or non-metallic but it, nevertheless, should have sufficient strength to carry the nozzle pressure loads during rocket firing. In selecting a material having sufficient strength to withstand loads during rocket firing, use is made of the fact that the nozzle wall automatically becomes structurally stififened by virtue of the outwardly directed pressure difference across the wall, An outwardly directed pressure exists forward of the transverse plane where the internal pressure equals the external ambient pressure. Aft of this point the pressure difference is inward and the nozzle collapses and does not transmit any loads to the rocket if the wall is infinitely flexible. Therefore, the material should have suflicient strength so that the portion of the nozzle wall aft of the point where internal pressure equals external ambient pressure will not be collapsed.

It has been found that thin metal such as tungsten or tantalum may be used for high temperature work or stainless steel or titanium for lower temperatures for instance up to 2000 F. The thickness of the metal may be from .001" to .250 according to the size and power of the rocket.

As best seen in FIG. 4 the expandable nozzle is fabricated from corrugated material 13. It can be appreciated that when the rocket nozzle reaches high altitudes where the gas pressure within the nozzle exceeds the external ambient pressure, the pressure difference across the corrugated wall of the nozzle is outward. Hence the outward pressure will act against the corrugated nozzle wall 13 and will expand the corrugated wall until the corrugations virtually disappear as seen in FIG. 3. The corrugated wall will be expanded more at the rear of the nozzle 12 than at the forward end, as seen in dotted lines in FIG. 1, resulting in a conically shaped nozzle since the wall will have less strength to withstand pressure loads at the rear of the nozzle than at the front end adjacent the fixed nozzle portion 10. It is seen, therefore, that this design permits the nozzle area ratio to increase automatically as the atmospheric pressure decreases In the nozzle shown the corrugation number 40, about 2" deep, rolled into a cylinder designed to open from a contracted diameter of 28 to an expanded diameter of 72" at the exhaust end. It will of course be understood that the specific details are given by way of example only and the invention is not limited to them.

The cylinder of corrugated sheet 13 may be assembled with flange 12 by pressing the forward end into flange 12, then forcing an inner ring 14 (FIG. 2) against the inside of the corrugated cylinder to deform the forward end against the mounting flange 12' after which the mounting assembly may be brazed into a unitary part.

In order to provide for stiffening and/ or cooling the adjustable nozzle a variety of expedients may be employed.

For most conditions a satisfactory solution to the structure problem is obtained merely by adjusting the wall thickness of the pressure stabilized curved sheet. Using metallic walls, cooling is obtained by radiation from the hot walls to the cooler environment around the rocket.

A more complex solution to the problem of stiffening the nozzle is to weld straight lengths of thin walled tubing 15 longitudinally to the inner surface of the nozzle similarly to the tubing arrangement shown in FIG. 3. This tubing arrangement provides a combination of convection and radiation cooling and would handle heat transfer conditions which are too severe for pure radiation cooling alone. For the cases where the heat transfer rate is even higher, the cooling must be accomplished by convection cooling techniques and/or film cooling almost exclusively. Film cooling refers to the technique of spraying coolant fluid onto the inside wall surface. Convection cooling refers to coolant flowing inside of coolant tubes. For a convection cooled expandable nozzle, the tubes would be arranged very close together so as to adequately cool all surfaces.

The tubing 15 is welded to the inner surface of the corrugated material 13 of the nozzle. The tubing is arranged in groups 16 of U form units 17 connected to the adjacent units at their outer and inner ends so that each group of five provides a continuous conduit from an inlet 18 to an outlet 19 As shown in FIG. 2 an inlet manifold 20 supplied with cooling medium by any suitable means and encircling the rearward end of the fixed portion of the nozzle 10 is connected through flexible jumper tubes 22 to inlet ends 18 of each group 16 of tubes. An outlet manifold 23 positioned against manifold 22 is similarly connected by jumper tubes 24 to outlets 19 of each group 16 of the tubes 17. Cooling medium, which in the case of liquid propellant rockets may be either the liquid fuel or oxidizer, or gas which is further used for other purposes such as pressurization of the rocket propellant tanks, may be circulated through the tubing 15 to cool the adjustable nozzle while in the case of a solid fuel rocket the cooling medium may be liquid or gas especially provided for this purpose.

In the embodiment of the expandable nozzle shown in FIG. a fixed portion 25 of a rocket engine nozzle is fitted with a flared skirt 26 of flexible heat resistant material such as reinforced rubber produced under the trademark GEN-Gard by The General Tire and Rubber Company or sheet asbestos reinforced with inconel wire and impregnated with an ablative material such as Teflon.

The skirt 26 of pliable material which comprises an automatically adjustable auxiliary nozzle portion has an upturned portion 26 clamped between a peripheral flange 27 on the outer surface of the fixed nozzle part 25 and a ring 28 by machine screws or bolts 29, and the free end of the skirt is tucked into the rear end of the fixed nozzle portion 25 such that the skirt 26 is folded upon itself in an inoperative folded configuration. The skirt material is thin and limp so that it may be laid against the inside face of nozzle portion 25, creases 30 projecting inwardly taking up the slack due to the greater diameter of the outer end of skirt 26 than of the fixed portion of nozzle 25 against which the inturned skirt is laid.

Firing of the rocket motor is effective to eject the tucked in portion of the skirt 26 after which the ambient pressure acting against the pressure of the exhaust issuing from the nozzle will determine the degree of opening of the skirt. Thus, the skirt 26 is movable from its inoperative folded configuration to an operative position where the skirt 26 forms an outwardly flared rearward extension of the fixed nozzle portion 25 which is of progressively increasing greater diameter than the fixed nozzle portion 25.

It should be appreciated that the flexible non-metallic skirt of the nozzle in FIG. 5 may also be bent up around the outside of the rigid nozzle section; however, in such a design the firing of the rocket chamber does not automatically open up the flexible section. Therefore, an auxiliary device would have to be used to pull the flexible nozzle backwards so that the rocket gas pressure could open it up.

Many variations of folding techniques are possible with the non-metallic flexible skirts.

Cooling of the skirt 26 may be secured for a limited time by radiation as well as spraying an ablative coating such as Teflon on the material of the skirt during fabrication or by impregnating the material of the skirt therewith.

The provision of an expandable nozzle has many practical advantages in addition to those previously referred to. For instance in the case of rockets carried by airplanes, the air drag is reduced compared to that caused by rockets fitted with nozzles of usual configuration.

The reduced diameter of the nozzle fitted with the expandable portion as compared with the usual rigid form of nozzle enables a larger nozzle opening, in flight to be obtained and permits use of larger combustion chambers under smaller pressure in the chamber with reduction in weight of the pressurized components, thus making it particularly advantageous for use under vacuum condi tions.

The expandable corrugated skirt of the adjustable nozzle of the invention is also adapted for use with the exhaust structure of special types of combustion chambers designed for vacuum operation and having a number of co-planar pressure fed burners grouped within a wide mouthed chamber; in this case the corrugated skirt is secured at its forward end to the lower edge of the chamber and in its retracted position extends around the fuel tank of a lower stage which is dropped after firing, thus leaving the corrugated skirt to be expanded on ignition of the pressure burners to serve as an automatically adjustable nozzle for the upper stage.

The automatically expandable nozzle of the invention is light in weight, free of any working parts, and inexpensive to fabricate. Also, it may be cooled by radiation or by circulating liquids or gases through tubular conduits serving also to take axial stresses, or by spraying liquid propellants against the inner surface of the nozzle in flight, or making a flexible nozzle from heat resistant material impregnated with ablative material.

Specific preferred embodiments of the invention have been described and shown herein by way of illustration and explanation of the invention, but not as limitative of the scope of the invention since various changes and modifications may be made in the described embodiments by those skilled in the art without departing from the scope of the invention as defined by the appended claims.

I claim:

1. In a rocket motor having a combustion chamber provided with a rearwardly directed outlet, a rearwardly extending rocket nozzle defining the outlet of the combination chamber, an automatically adjustable auxiliary nozzle portion comprising a skirt of pliable material secured at one end thereof to said rocket nozzle and being folded upon itself in an inoperative folded configuration, and said skirt of pliable material being movable from its inoperative folded configuration to an operative position where said skirt forms an outwardly flared rearward extension of said rocket nozzle which is of progressively increasing greater diameter than said rocket nozzle.

2. In a rocket motor as set forth in claim 1, wherein said one end of said skirt secured to said rocket nozzle is disposed in surrounding relation thereto, and said skirt including a skirt portion superimposed on said rocket nozzle rearwardly of said one end of said skirt such that said skirt is folded over the rear end of said rocket nozzle and extends within said rocket nozzle in a tucked-in condition in its inoperative folded configuration.

References Cited UNITED STATES PATENTS 2,569,996 10/1951 Kollsrnan 239-534 X 2,645,999 7/1953 Bogard 60271 X 2,758,755 8/1956 Schafier 222-490 X 6 2,901,183 8/1959 Kohl 239205 2,940,251 6/ 1960 Prentiss 239534 X 3,210,929 10/1965 Thomanek 60271 X FOREIGN PATENTS 126,325 5/ 1919 Great Britain.

M. HENSON WOOD, JR., Primary Examiner.

VAN C, WILKS, Assistant Examiner. 

1. IN A ROCKET MOTOR HAVING A COMBUSTION CHAMBER PROVIDED WITH A REARWARDLY DIRECTED OUTLET, A REARWARDLY EXTENDING ROCKET NOZZLE DEFINING THE OUTLET OF THE COMBINATION CHAMBER, AN AUTOMATICALLY ADJUSTABLE AUXILIARY NOZZLE PORTION COMPRISING A SKIRT OF PLIABLE MATERIAL SECURED AT ONE END THEREOF TO SAID ROCKET NOZZLE AND BEING FOLDED UPON ITSELF IN AN INOPERATIVE FOLDED CONFIGURATION, AND SAID SKIRT OF PLIABLE MATERIAL BEING MOVABLE FROM ITS INOPERATIVE FOLDED CONFIGURATION TO AN OPERATIVE POSITION WHERE SAID SKIRT FORMS AN OUTWARDLY FLARED REARWARD EXTENSION OF SAID ROCKET NOZZLE WHICH IS OF PROGRESSIVELY INCREASING GREATER DIAMETER THAN SAID ROCKET NOZZLE. 